1. Field of the Invention
The present invention relates generally to multiple-band (multi-band) wireless communication devices and systems. More particularly, the present invention relates to multi-band mixers and quadrature signal generators useful in multi-band wireless receivers of wireless communication devices.
2. Description of the Related Art
As the field of wireless communications continues to develop at a rapid pace, the resulting increased number of systems and frequency bands in use continues to complicate the delivery of wireless communications to consumers. In many cases, network operators providing services on one particular frequency band have had to add service on additional bands to accommodate its customers demand for wireless service. Further, the carriers have had to deploy multiple wireless communication systems using different technical standards. Accordingly, advanced communication devices, such as cellular radio telephones, must be able to communicate at multiple frequencies pursuant to multiple technical standards to enable communications on the varied wireless communication systems the device may encounter.
Dual- or multi-band telephones are particularly desirable where the different wireless communication systems operate at different carrier frequencies or frequency bands, but use the same modulation scheme and baseband processing scheme. The well-known Global System for Mobile communications (GSM), Personal Communication Services (PCS), and Digital Communication System (DCS) systems share such similarities, for example. Moreover, in today's digital mobile radio systems, more than one frequency band is available for RF (Radio Frequency) transmission. For instance, GSM in Europe uses two frequency bands of 25 MHz bandwidth centered at 900 MHz (GSM 900) and 1800 MHz (GSM 1800), respectively, where each of these frequency bands comprises an up-link (information transfer from mobile station to base station) and a down-link (information transfer from base station to mobile station) frequency band. In the United States, these two GSM frequency bands are centered at 850 and 1900 MHz respectively. GSM also provides for each of the up- and down-link bands to include a plurality of Frequency Division Multiplex (FDM) sub-band RF channels of 200 kHZ bandwidth each. Accordingly, a dual-band GSM mobile phone is capable of transmitting and receiving both the GSM 900 and GSM 1800 bands.
An exemplary prior art dual-band radio-receiver is shown in FIG. 1, where RF signals transmitted from a base station are received by the receiver at an antenna 10, which passes the RF signals to a band splitter 30, which splits the received signals into first and second (or more) bands. First and second band pass filters (BPF) 12a and 12b filter the split signals in the first and second bands, respectively, permitting the receiver to receive in each of the two separate communication bands. The filtered signals output by BPF 12a, 12b are supplied to quadrature demodulation (demod) units 32a-32b, respectively, which convert the band pass-filtered signals into in-phase (I signal) and quadrature (Q signal) baseband signals for further processing. The quadrature demodulation units 32a-b include low-noise amplifiers (LNA) 34a-b, dividers 20a-b and mixers 40a-b. The dividers 20a-b divide the intermediate frequency signal received from the local oscillators (LO) 36a-b to create intermediate divide=by-2, divide-by-4 signals having a phase difference of 90°. A first mixer (mixer pairs 40a, 41a) and a second mixer (pairs 40b, 41b) mix the generated LO signals with the amplified received signals to generate the I and Q baseband signals, which are low-pass filtered by in-phase low pass filter 42a and a quadrature low pass filter 42b, respectively. The filtered I and Q signals are then passed to baseband processing circuitry 44, which is conventional baseband processing circuitry as is well-known in the art.
As will be appreciated by reference to the receiver of FIG. 1, it is difficult to provide a multi-mode radio receiver for processing signals at multiple frequencies without duplicating many receiver hardware components. In the prior art, separate band pass filters, dividers, local oscillators, mixers and low pass filters for each serviced frequency band are designed into the receiver. Accordingly, it would be desirable to provide a receiver for a wireless communication device capable of receiving signals at multiple frequency bands, while minimizing the power consumption and duplication of receiver hardware.
In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced.